So the factory standard setup is stop/start/regen with AGM starter battery, ok, so i ask the sales guy why i haven't got a second AGM battery under the passenger seat, (for balanced charging from regen etc).... he goes and gets a technician. ..... The tech says thats totally normal and supposed to be that way. i mentioned about the 80% charge levels for regen etc and about the relay for split charging!!! all totally normal he says......? Now im confused...have VW got it all wrong? surly not?

He then goes on to tell me that as long as the BCM etc is programmed for the leisure battery then the charging system etc is fine. The 100A split-charge relay is fine. the 80A supply fuse is fine, The lead-acid leisure battery is fine. The AGM starter battery is fine......All is good in the world...........

BUT !!!!!!! he did say that the problems come from people who have fitted the leisure battery/split charge setup themselves as the BCM hasn't been programmed for that scenario and the charging strategy isn't assuming the extra load of charging the second leisure battery......? (plausible i thought)

So i left the dealers with the van now more confused than ever. My questions to myself..

Do i need AGM batteries for both starter and Leisure?
Do i need a third party DC-DC charger?
Is the factory split charge relay good enough?
Do i fancy a ham sandwich?
Beer or Cider tonight?
............................hmmm decisions decisions.....

i decided to do my own research ..........

below is the factory AGM battery.

and the close-up

here is the factory split charge relay setup:

the 100A relay and 80A supply fuse.
this is the factory leisure battery:

So thats the factory setup,

now here is the test results, these were gathered from two voltage data-loggers, one connected to the main starter battery and the second across the leisure battery.... over a 3hour period of the test drive, which included starting/stopping/regens/city and A road driving plus a half hour park up for good measure,

below is the readout for the main AGM battery

and below is the readout for the Leisure battery:

here is my conclusion from what i can see...

The leisure battery is disconnected at initial engine startup so no effect on it at startup.

The smart alternator seems to have gone to a high output setting @ 14.8v , presumably while the engine is warming up and boost charging the battery (and leisure battery) for the first 15-20mins of the drive cycle.(i may have had the heated seats on too?)

when start/stop kicks in, the leisure battery stays connected but is un-effected by the starter drain (low 10v when cranking), im assuming that the factory DC-DC charger keeps the voltage up and stabilized while the starter is cranking.

The regen breaking phases show charging spikes of around 14.8v accross both the starter and leisure battery's. (obviosly as they are both connected via the split-charge relay)

The average voltage the leisure battery sees is above the 12.6v assumed for as a charged battery (about 12.8v - 13-8v)

From what we can see the factory split charge setup seems to be up to the job for the basic battery . . . . . . . .

But im going to assume that old-skool charging would be way better for the AUX battery. A fixed 13.8v constant charge would be more beneficial at keeping it charged compared to the spiky pulsed charge its getting from the regen (plus bulk charge after starting)......so the DC-DC charger would help here.

one next test i need to do is run the AUX battery low/flat and see what happens then?.........basically will it receive enough charge, or will it charge up well enough after a drive?

The upgrade would be Dual AGM batteries and a third party DC-DC charger im assuming.

if/when i upgrade ill redo these tests and see what the difference is.....

Improved flooded battery technology, increasingly referred to as EFB technology in the market, offers a cost effective solution for entry level Start-Stop vehicles. EU emissions targets for these vehicles are lower than those set for higher performance models. This has led to manufacturers developing a battery technology that meets the demands of Start-Stop operation in a higher state of charge than expected from AGM technology, but lower than that expected from standard wet-flooded starter batteries.

To meet the growing demand for OEM specification EFB technology in the European aftermarket, Yuasa has introduced 11 new EFB battery types with the launch of the YBX7000 Start Stop range. This range comprises 5 European (DIN) and 6 Japanese (JIS) battery sizes to maximise coverage of vehicles in the UK parc.

In addition to Start-Stop, Yuasa EFB batteries are well suited to use in demanding applications. In repetitive deep discharge scenarios, such as those common to Police vehicles and Taxis, EFB technology offers improved cyclic durability, when compared to premium wet-flooded batteries.

Frequently Asked QuestionsQ. What are the differences between standard flooded and EFB batteries?
A. EFB batteries are an enhanced version of standard wet-flooded technology. The primary benefits of EFB technology are improved charge acceptance and greater cyclic durability when operating in a reduced state of charge (typical of Stop Start applications). As an approximation, EFB batteries will provide 85,000 engine starts, compared to 30,000 starts from standard flooded product.

Q. What are the differences between EFB and AGM batteries?
A. EFB batteries have been introduced as a lower tier option to AGM batteries in terms of performance and durability. EFB technology relies on improvements to existing flooded technology through the addition of Carbon additives in the plate manufacturing process. AGM batteries benefit from the inclusion of unique design features not found in wet-flooded batteries. These include glass mat separators, recombinant lid technology and higher pack pressures to facilitate improved cyclic lifespan. AGM batteries are better suited to meeting the demands of higher specification vehicles that include one or more of the following technologies: Start Stop, Regenerative Braking and Passive Boost.

I agree that batteries being charged from the same source should be of the same charging characteristics and the leisure batteries in the California are all 3 AGM.
What you haven’t seen yet that I measured, was there is also a mode when the alternator idles and current flows back from the leisure side to supplement the vehicle side and that is why I removed the factory 150 relay for a DC-DC system.

For anyone thats interested ive gone another voltage "data logging" today, but with a slight difference.

Ive done it with the "Drive to work" as normal with stop/start enabled,

And the drive home with "stop/start" disabled

Both trips are about 2 hours drive time with a good "parked up time" between.

I done this because i was interested to see what the difference in charging strategy would be for the "stop/start enabled" VS "stop/start disabled" on both the starter and AUX battery using that OEM Factory split charge relay setup.

The results were a surprise.

This is the main starter battery read out. >>>>>

You can see the same as before with the stop/start/reg mode, but when the stop/start was disabled the charging strategy was not what i expected........

I expected that the default strategy would be like Euro5 with the alternator outputting 13.8v constant to charge the battery's. But the reality is that the regens still occur and the alternator does not charge by itself unless the BCM commands it.

So whether you have stop/start enabled or not the battery charge strategy is still the same..... Regens to keep pulse charging the battery.

Now i have noticed that there is a way to FORCE a high charge rate from the alternator, and that is to switch on a high current demand circuit. with me if i switch on the heated seats or heated front windscreen the charge voltage will rise from 12.6v battery float voltage to the 13.8v standard charge voltage.....also whilst doing this the regens still take effect and will rise the 13.8v to 15.0v.....
when you switch off the high demand circuit things go back to normal and a 12.6v battery float voltage.

This is the read out for the AUX battery >>>>>

You can see the same here...... the charge level and voltage is exactly the same as the main starter battery as the are connected via the OEM Factory split charge relay.....

but what you dont see is the restarts when in start/stop mode...... this is because the factory DC-DC converter kicks in for the brief starter motor dwell time and smooths out the power.

so that proves that although the starter and AUX battery ARE connected via the factory relay, the AUX battery is connected to the output side of the DC-DC converter, that why we can see the restart drops on the starter battery and not on the AUX battery.

FYI all tests were done at the battery posts on both batteries to get the real results.

I think some of the readings are misunderstood. 12.6 is not a float voltage, it is off charge and 13.8 is the float. A bigger load such as A.C. should provoke 14.4 volts and will also lock out stop/start. I also think that the reason that you don't see the starter motor load on the aux battery is because the relay opens during cranking. What we used to know as X relief. There are clearly differences between the factory specced aux battery system and the Cali type system so there is plenty going on in the programming dept. How did you get on with the Redarc?

I think some of the readings are misunderstood. 12.6 is not a float voltage, it is off charge and 13.8 is the float. A bigger load such as A.C. should provoke 14.4 volts and will also lock out stop/start. I also think that the reason that you don't see the starter motor load on the aux battery is because the relay opens during cranking. What we used to know as X relief. There are clearly differences between the factory specced aux battery system and the Cali type system so there is plenty going on in the programming dept. How did you get on with the Redarc?

Click to expand...

yes my bad in the description, 12.6v is the static battery unloaded "after surface charge" and not a float charging voltage.......most of the time the battery is not being charged at all..

and it seams that the starter load is isolated from the AUX battery via the DC-DC converter (Voltage stabilizer) ..... maybe? but cant see the full current flow on the schematic.

"terminal 30 is fed through a DC/DC converter during the starting process and the voltage is stabilised at 12V.", so somehow the termoinal 30 stabilized voltage must be diverted to the aux battery also? unless the AUX relay IS disconnecting and reconnecting as you mention during restarts......ill have to do some more tests to see if thats the case or not.

ELSAWIN Quote:
Role of voltage stabiliser:
Voltage dips occur in the onboard supply system each time the engine is started due to the high current draw of the starter. To prevent any failure in the infotainment components and the dash panel insert when the engine is restarted, the voltage supply to the infotainment system and the dash panel insert is protected by means of voltage stabilisation. To do this, terminal 30 is fed through a DC/DC converter during the starting process and the voltage is stabilised at 12V. The DC/DC converter is only active during the actual starting process (terminal 50). For other times, the converter is bridged with the aid of an internal relay and supply comes directly from the onboard supply system (terminal 30).
Effects in case of voltage stabiliser failure:
When the starter is operated and the voltage supply is insufficient for devices like radio, radio navigation or telephone they will perform a reset. If, in start/stop mode, the mentioned electrical consumers are identified as causing a reset for each motor start, this indicates a defective voltage stabiliser. A direct entry concerning a malfunction of the voltage regulator, e.g. in the event memory of the diagnostic interface or the onboard supply control unit, does not occur at present. If radio, radio navigation and telephone units fail together, first check fuse of voltage regulator.

looks like the voltage stabiliser is by the ECU at the front left under the battery area:

and the voltage stabilizer description:

Redarc not fitted yet....still waiting for the extra bits i needed. battery terminals/fuses/fuse holders and the like.... soon hopefully.

As I said way back in the thread, the voltage stabiliser has nothing to do with the charging of the aux battery. Its only for the voltage sensitive devices like the infotainment system and the instrument cluster etc.

As I said way back in the thread, the voltage stabiliser has nothing to do with the charging of the aux battery. Its only for the voltage sensitive devices like the infotainment system and the instrument cluster etc.

Click to expand...

cool, that answers that. ill do some tests on the OEM relay to see if it drops out on restarts.

The data i was looking for, Done a voltage logging chart of the main starter battery VS the BCM controlled AUX relay. to see whats going on.

you can clearly see that the BCM shuts of the relay during the stop/start phases and reconects after the engine has started.

starter battery log >>>>>>

and now the Proof >>>>>

There way have it . . . . .

So those poor relays for the stop/start and BCM AUX battery relay are getting a good hammering ALL DAY, wonder how long they will last? or what there MTBF is? And if ir was worth replacing them with solid state relays?

My redarc is working brilliantly, just had 2 weeks away with a few 2 nighters without hookup and with 2 batteries charged fully was able to run fridge and a separate freezer and charge phones etc without any issues.

ive got two CTEK battery monitor units - one on each battery (main & AUX) , the main battery stays at about 80% average using stop/start enabled 100% 0f the time with a 80/20% (city/motorway) driving style.

the AUX battery was always <30% in charge level.

Also as mentioned on here before the AUX battery would DISScharge itself back into the starter battery when the split charge relay was enabled.

As for stop/start i now keep it switched on all the time, im happy with the perceived/actual fuel savings and have now adapted my driving style to take into acount the start/stop delay at say roundabouts and junctions.

CTEK monitors look good - although I've already started my own private collection of Victron products. It was through installation of 150 PV panel and Victron Smart MPPT that I found out about the issues with T5/T6 Bluemotion.